Method and apparatus for synchronized drives



METHOD AND APPARATUS FOR SYNCHRONIZED DRIVES Filed 001;. 20, 1958 G. E. MATHIAS ETAL 9 Sheets-Sheet 1 CBw o 959: 222: N 9m 50 m 55mm 0 k 230 umom 4 30 x 23w wBucE E 222 E m .0333 E; 5 59.95. umwm All 39: gm

INVENTORS Roberi W. Egglesione Gerald E.Ma1hiqs 8 Charles G. Helmlck WITNESSES 7% 6 W ATTORNEY Feb. 19, 1963 3,078,402

METHOD AND APPARATUS FOR SYNCHRONIZED DRIVES Filed Oct. 20, 1958 G. E. MA THlAS ETAL 9 Sheets-Sheet 2 Feb. 19, 1963 G. E. MATHIAS ETAL 3,073,402

METHOD AND APPARATUS FOR SYNCHRONIZED'DRIVES Filed Oct. 20, 1958 9 Sheets-Sheet 5 CONTROL UNIT Feb. 19, 1963 G. E. MATHIAS ETAL Filed: Oct. 20, 1958 9 Sheets-Sheet 5 Fig. 5

Primary Primary Primary VLI VLI VLl VL3 VL2 VL3 VL2 VL3 VL2 a b c Secondary Secondary Secondary VllTP Vl2TP VI3TP d VZITP V22TP f V23TP Fig. 7

v 1'p VIZTP VI3TP V2ITP V22TP V23TP a b c VHTP 3V|TP V22TP V2|TP V23TP V|2TP V2TS 3V2TP VITS VI3TP Feb. 19, 1963 e. E. MATHIAS ETAL 3,078,402

METHOD AND APPARATUS FOR SYNCHRONIZED DRIVES 9 Sheets-Sheet 8 Filed Oct. 20, 1958 I. "a; l "mm; 5%

if I; 2 2

0 ma MI- o 02 Q2 3 mm B 5 B i n? 5 MW? mm MU mm m MT? mm@ W a U 6 Feb, 1963 e. E. MATHIAS 'ETAL 3,07

METHOD AND APPARATUS FOR SYNCHRONIZED DRIVES United States Patent This inventionrelatcs to the control or regulator art and hasparticular relationship to the control or regulationof drives which are subjected to heavy loads that may vary over a wide range during eachcycle of operation. Application Serial No. 670,318, filed July 5, 1957 to Gerald E. Mathias and Robert W. Egglestone for Synchronized Conveyor Control and assigned to Westinghouse Electric Corporation is incorporated in this application by reference.

The apparatus to which the invention disclosed in this application is particularly applicable is typified by a line of progressively operating presses which form work, say metal sheet, intoa finished product, for example, a body part of an automotive vehicle. Such apparatus includes aplurality of dieson each of which the work is subjected to pressure exerted by a press. The work after being ,treated on one die is moved-from this die to a succeeding die and following each movement is subjected to pres sure by the press of the new die until after treatment in the last die o-fthe series, the final product is achieved. Each press is moved continuously by amotor driven crank mechanism repeatedly engaging and formingthe work.

As each press engages the work it exerts increasing pressure on the work untilthe press passes through a deadcenter position where it exerts the maximum pressure onthe work.

Each press drive is provided with a flywheel which stores energy during the part of a cycle during which the drive is lightly loaded and releases energy during the part of the cycle during which the drive is loaded.

The loading imposed on the press drives by the difier- -ent presses may be relatively high. For example, in a typical situation, the loading may be 1200 inch-tons.

Each press drivemust becapable of delivering substantia1-power,-say of the order of 400 to 1000 horsepower. It is desirable that the work be produced at a relatively high speed and the presses rnust operate-at a correspondingly high speed. A speed of 25 strokes or cycles per minute foreach press is typical.

It is desirable that all presses work together in forming the work and that thepresses be so synchronized that their compression operations be carried out after the Work has been properly seated. on the die .and the mechanism for advancing the work has been retracted to its standby position and it is broadly-an-object of this invention to provide a. method and apparatus for accomplishing such synchronization.

In arriving at this invention, it was realized from a study of the operation of the apparatus to be controlled that this apparatus has certain highly unusual operational features. Each drive passes through a cycle during one part of which its associated press is compressing or otherwise drawing, forming, or trimming the work and during another part of which its associated press is moving away from the Work and the work is being advanced. During the forming part of the cycle, the press and its drive are heavily loaded and during the work-moving part of the cycle, the press and its drive are very lightly loaded. During the loaded part of the cycle, the drive maybe constrained to move at a. low speed and during "the unloaded part of the cycle the drive isfree to move 3,078,402 Patented Feb. 15, 1963 at a relatively high speed, the ratio of the latter speed to the former speed may be of the order of 2 or 3:1. I

During a complete operation the loading of any press relative to the others may vary over a wide range. At the start of an operation, the raw material for the first work item is seated on the first die while the others-are unloaded. One press is at this time heavily loaded while the other presses are unloaded. During the succeeding cycle two presses are loaded while the others are unloaded. This continues until all the presses are loaded. with all the presses loaded, the loadon the different drives during the loading part of each of the cycles may vary Widely. One of the presses may be carrying out a forming or drawing operation and subjecting its drive to a heavy load while at thesam e' time another of the presses may be performing atrimining operation subjecting its drive to a relatively low load. At the completion of a series of operations, thepresses are gradually unloaded in the inverse order to their loading during the start of an operation. v i i Under these variable loading conditions, it is desirable that .the presses and their drives be. synchronized. Syn- .chronization bymechanically linking the ,drives is not satisfactory because the linkages are subjected to enormous stresses and diificulty is encountered in providing adequate-linkages which are capable of responding with the speed required to the changes in the loading of the drives.

It is then a specific object of this invention to provide a method and apparatus for synchronizing a plurality of mechanically v disconnected drives. which are subjected to highly variable loads of high magnitude that may be different for the .dilierent'drives. I

Another specific objectof this invention is to provide apparatus for synchronizing a plurality ofdrives which are not connected mechanically but ,whichare required tooperate together and which are subjected to highly variable loads Whichmay differ forthedilierent drives.

A further specific object ofthisinvention is to provide a method and apparatus for coordinating the speeds and the positions of a plurality-ofdrives subjected to highly variable loads sothat the drives operate together in the desired manner.

An incidental object of this invention is to provide a novel method. of speed control having general applicability but particularly suitable for the coordination ofthe operation of a plurality of drives-which are operated together .but which are subjected to highly variable large loads diiferent for the different drives.

Another incidental object'of this invention is to provide a-novel. method of controlling the speed of a plurality of drives, the operation of which is to be synchronized so that theyv operate together and which are subject to highly variable largeloadsdiilerent for the diiferenhdrives.

This invention arises from the realization that the drives need not be maintained at the same speedsandat the same relative positions duringtheir entire cycles ofoperation. It is only necessary that the speeds and relative position of the drives be suchthat they startthe c ornpressing operation together at a prescribed speedand that they repeatedly reach the starting speed priorto the start of each of the succeeding compressing operations. a It has been realized then that therdrives-may bepermitted to reach diilerentspeeds andtobecomedisplacedin position with reference to each other to a limited extendduring the loaded part of the cycle provided that they are reset to operate together at a set speed during the unloaded part of the cycle.

In accordance with this invention inits specific aspects the drives include no mechanical interconnection butare provided with electrical interconnections which permit aoraees the speeds of all drives to decrease once the speed of at least one of the drives drops below a predetermined set magnitude. This limits the position deviations of the drives from each other. As to the position deviations which do occur, the electrical interconnections operate in dependence upon the position deviation of each drive fromthe average position of all ofthe drives to bring the drives to the same relative positions. The corrections in speed and position are etfected during the unloaded part of the cycle so that the drives are positionally and in speed together just before the loaded part of the cycle starts.

In accordance with a specific aspect of this invention, speed control apparatus is provided which includes a master speed reference for all of the drives. This speed reference cooperates with regulators connected to each of the drives to tend to maintain the speed of each of the drives at a magnitude corresponding to the reference so long as the speed of all drives is above a predetermined magnitude. When the speed of any drive drops below this predetermined magnitude, a portion of the master speed reference parameter is absorbed externally to the regulators so that the regulators all operate to tend to adjust the speeds of the drives to a new reference corresponding to the lower speed of the drive which has dropped to a speed below the predetermined magnitude. When the speeds of all the drives returns to the predetermined magnitude, the master speed reference parameter again becomes effective and the drives are returned to the speed corresponding to this master reference. For this purpose, it is important that each of the drives be supplied with power and be capable of drawing adequate power for the necessary acceleration from the lower speeds to the speed corresponding to the master reference.

In actual practice, the speed of one or more of the drives drops below the predetermined magnitude during the loaded part of the cycles. All drives are then permitted to drop to a lower speed by the reduced speed reference parameter. During the unloaded part of the cycle adequate power is supplied to the drives to produce the necessary acceleration to return the drives to the speed corresponding to the master reference. At the start of the succeeding loaded cycle the drives are then back to their original speeds.

The novel features considered characteristic of this invention are disclosed generally above. The invention itself both as to its organization and as to its method of operation together with additional objects and advantages thereof will be understood from the following description of a specific embodiment when read in connection with the accompanying drawings, in which:

FIGURE 1 is a diagrammatic view showing a drawing, blanking or coining press line to which the invention disclosed herein is applicable;

PH 2 is a diagram showing the operation of the process line illustrated in FIG. 1;

FIG. 3 is a circular diagram showing the angular extent of the different parts of the cycle of a press of the apparatus illustrated in FIG. 2;

FIGS. 4A, 4B and 4C together constitute a circuit diagram of a preferred embodiment of this invention With which the method in accordance with this invention may be conveniently practiced;

FIG. 5 presents vector diagrams corresponding to the position following elements or synchroties of FIGS. 4A, 4B and 4C;

FIG. 6 presents a series of vector diagrams showing the vector relationships of the potentials derivable from the position following elements of FIGS. 4A, 4B and 4C;

FIG. 7 presents a series of vector diagrams illustrating the vector relationship between the potentials derivable from the position following elements when the positions of certain of these elements are displaced with respect to the others;

FIG. 8 presents a series of vector diagrams showing the potentials derivable from the position following elements under the conditions illustrated in FIG. 7;

FIG. 9 is a circuit diagram illustrating in detail the speed control system of the apparatus shown in FIGS.

4A, 4B and 4C; and

invention particularly applicable to a two-drive line.

T he apparatus shown in FIG. 1 is a press line including a plurality of dies on which work W1, W2 and W3 is to be formed. The work may be moved onto the leadare movable relatively to the bars 23 into engagement with the work and the bars 23 are movable to advance the ting rs 2.1 with any work they are carrying or to return the fingers for each now advancing operation.

Each press (not shown) of the press line is actuated by a crank (not shown) which operates continuously as it is continuously driven by an associated drive. The cycle of operation of a press (not shown) of the press line is shown in 2 and PEG. 3 shows the circular movement of the driven end of the crank (not shown) which drives a press in a typical situation. FIG. 3 is labeled to correspond to FIG. 2 and in addition it includes the points BBC, the bottom dead center at which the work is subjected to the highest stresses, and TDC, top dead center where the press is most remote from the work.

it is assumed that in FIG. 1 the fingers 21 are in a position where they have seated the work W1, W2, W3 on the dies and are about to be retracted. This corresponds to points A of FIGS. 2 and 3.

The fingers M are retracted between A and B of the cycle and the return of the bars 23 to the back position is started. During this part of the cycle the presses move toward the work W1, W2, W3 engaging the work at a point in the cycle corresponding to B. Between parts B and BBC of the cycle the work is formed on the dies. etwecn BBC and C the presses are retracted. At point C, the bars 23 are in the extreme retracted position and the fingers 2T. are moved out to engage the Work. At point D, the fingers 21 are in engagement with the work. The leading fingers 21 are in engagement with raw material to be deposited on the leading press; the fourth set of fingers 21 with W3 which is finished.

etween D and A the work is seated on the successive dies. While the fingers are moving as described, the presses are moving from positions corresponding to C to position A.

The compressing and retraction movements of the presses takes place during the part of the cycle repre sented by the arc BC. In a typical case, the arc BC subtends an angle of Thus, the compression part of the cycle constitutes about /2.; of the complete cycle. The fingers 21 are moving into or out of engagement with the work between parts C and D and A and B of the cycles and during these parts the presses must be out of the way.

This invention arises from the realization that it is not essential that the presses be so synchronized that they are together continuously througout the cycle or stroke. It is only necessary that the presses be properly positioned so that the compression part of the cycle starts when the work is properly seated. That is, the presses should be together at instant B. At instant C, the positions and speeds of the presses may have departed from synchronization to a limited extent. The departure must not be such that any press is in the path of the fingers 21 as they start in. The presses are brought 10 is a circuit diagram of a modification of this 1 and a shunt field winding 3 auras-o2 back together as the drives move during the unloaded part of the work cycle between positions C and B.

In practice the bars 23 and fingers 21. are mechanically linked to one of the presses, for example, the one corresponding to work W1. The drives for this one press and the others are linked electrically in such a way as to permit substantial change in speed and position during the loaded part of the cycle and correction during the unloaded part. In a typical situation in which the loading is 1200 inch-tons and the speed of the presses is 25 strokes per minute, the speed may drop as much as 5% during the loading part of the cycle, and the relative positions of the drives may change correspondingly. For the same loading where the rate of operation of the presses is 12.5 strokes per minute, the speed may drop as much as and the relative positions depart correspondingly.

The apparatus shown in FIGS. 4A, 4B and 4C with which the invention is practiced includes a Drive Unit and a Control Unit. This apparatus is supplied from conductors L1, L2 and L3 which are energized from a commercial alternating current supply through the usual disconnects or circuit breakers (not shown).

The Drive Unit includes drives DRI, DRZ and DR?) each of which has a drive motor M connected to control a crank (not shown) which drives the corresponding press. The Control Unit operates to control the speeds of the motors M so that the positions of the motors of the drive units are properly related to the operation of the fingers 21.

Each drive D'Rll, DRZ and DR3 includes in addition to the motor M a generator G for energizing the motor, a tachometer or pilot generator PG, a speed reference generator or exciter GS and a magnetic amplifier MA for controlling the motor M. The motor M has a shunt field winding which may be energized from a directcurrent supply. The supply is indicating only symbolically but usually derives its power from the conductors L1, L2 and L3 through a rectifier. The positive and negative terminals of the field supply are connected to the field winding 25 through a variable resistor 27 which serves to derive a potential proportional to the field current. The generator G has a series field winding 29 The operation of the motor M is controlled primarily by controlling the current flow through the shunt field winding 31. This i elfected by the magnetic amplifier MA. The pilot generator PG has a shunt field winding 33 which is supplied from a direct-current supply. The speed reference generator GS also has a shunt field winding 35 which is supplied from a direct-current supply through a variable resistor 37. The resistor 37 serves to set the speed refing WB, a damping winding WD and a current limit winding WCL. The output winding W0 is center tapped. This winding is supplied from the conductors Ll and L2. These conductors are connected to the shunt winding 3 1 of generator-G through the winding W0 and through rectifiers id, 43 and 45 which assure that the current flow through the windings W0 is of such polarity as to produce a self-biasing effect characteristic of magnetic amplifier operation. The winding WC is sup plied from the Control Unit.

The control of the speeds of the motors M of the three drives DRl, DRZ and DR3 is interdependent. The connection of the speed reference windings WSR and the speed windings WS of the magnetic amplifiers MA of the three drives is not individual to any one drive but involves all drives. This connection is shown in FIG. 9. The speed reference winding 'WSR of each of the magnetic amplifiers MA is supplied from the generator GS, in a circuit extending from the positive terminal ofthe generator through amaster variableresistor 51 .and associated variable resistor 53 individual generatorto the negative terminal.

to each winding, the winding WSR to the negative terminal of the exciter GS. The exciter GS is also .con-

nected in a circuit with each of the pilot generators PG. This circuit extends. from the positive terminal of the generator GS through the variable resistor 51, a rectifier 55 individual to each generator PG,'the pilot The speed winding WS of each of the magnetic amplifiers MA is supplied from. the associated pilot generator PG in a circuit eX tending from the positive. terminal of the generator, PG through a variable resistor 57, the .Winding WS to the negative terminal. The rectifiers 55 are so poled that so long as theassociated pilot generator PG produces a voltage of a predetermined magnitude, current fiow through the resistor 51 and through the pilot generator from the speed referenceGS is blocked. Thus, thefull voltage of the exciter GS is available as a speed reference.

The ampereturns produced through WSR by the volt age of GS is balanced against the ampere turns produced through windings WS by the associated pilot generator PG. Thewindings WSR and WS are so poled in each magnetic amplifier that the higher the ampere turns of WSR, that is, the higher the Voltage ofGS, the higher the voltage of PG required to counteract the ampere-turns of WSR. The voltage of PG depends on the speed of the associated drive M.

Thus, the higher the voltage supplied from exciter GS the higher the speed that a drive M is permitted to reach. As the total voltage of the exciter GS serves to set the speed reference, the motors M are permitted to reach the maximum speed. The motors M are thus. permitted to reach the maximum speed so long as all pilot generators PG supply a voltage above a predetermined magnitude.

When any of the motors M drops to a speed such that its pilot generator PG puts out a voltage lower than the magnitude, current fiows through the master resistor 53., the associated rectifier andthe generator absorbing part of the voltage from the exciter GS available for speed reference. :The speed reference is thus reduced for all motors M and motors are permitted to drop to a lower speed.

The winding WB is supplied from a suitable direct current source which may be varied to produce the desired bias. The damping Winding WDhas the function of suppressing oscillation of the generator G in response to surge. This winding is connected in a circuit with the generator G which extends from one terminal of the winding through a surge suppressing capacitor 61, the generator G, the series field winding 29, a resistor 63 to the other terminal. The current limiting winding WCL is connected in circuit with the series field winding 29 of the generator C and a rectifier 65. The rectifier 65 is of the bridge type with two of its opposite terminals connected across the variable resistor 27 in series with the shunt field winding 25 of the motor M and the other opposite terminals connected.

in series with winding WCL, a resistor 67 and the-series field winding 29. Current can only flow through the Winding WCL if the potential across the series field winding 29 exceeds the potential'impressed by the variable resistor 27. The variable resistor may be so set that when the current through the series field winding 29 is excessive, current'flows through WCL reducing the current flow through the armature of the generator G and the series field winding 29.

The magnetic amplifiers MA of the drives DRL DRZ and DR3, the generator G and the motors M are controlled in dependence upon the relative positions of the drives through the windings WC of the magnetic amplifiers MA which are controlled from corresponding componnets oi the Control Unit. The Control Unit includes a plurality of synchrotiesSYl, 5Y2 and 8Y3 which are, in effect, rotary transformers capable of producing a position reference signal. Each synchrotie has a three-phase rotor 71 and a two-phase stator '73. The brushes of the rotors Ill are connected to conductors Ll, L2 and L3 respectively and are thus supplied with three-phase potential. Two-phase potential, the components of which have phase positions dependent on the positions of the rotors 71, is then derivable from each stator 73. Each synchrotie has two pairs of terminals 75 and 77 and '79 and 3 Single phase alternating potential is derivable from each pair and the potential for one pair of each synchrotie is displaced in phase by 90 with respect to the potential of the other pair.

The rotor ll of SYl is mechanically connected to the motor d of drive DRE, the rotor of SYZ to the motor M of DRE and the rotor of 8Y3 to the motor M or"- DRE). The connection may be directly to the motor M in each case or to the crank which drives the associated press. The connection in each case is rigid so that the rotor of the synchrotie has a position corre sponding to the position of the crank or to the position of the corresponding press.

T he Control Unit also includes transformers ll'i, l' T, 131 and 23.1", 221" and 231'. The primary ilTP of HT is connected to one pair of terminals 7577 of; SYl, the primary iii 1T? to a corresponding pair FE- 77 t SYE and the primary EST? to a corresponding pair '75-'77 of 8Y3. Primaries llTP, lZTP and 131'? then carry alternating current supplied by the associated synchroties respectively and displaced in phase in dependence upon the angular displacements of the rotors of the associated synchroties from initial settings. The primarries ZlTP, ZZTP and are similarly connected to the other pairs of terminals '7 l or Srl, 5Y2 and 5Y3 respectively. Each transformer llT, 1.2T, EST, 2311", 5.2T, 23?." has a pair of secondaries llTSl and ill S2, 1ZTSI. and lZTSZ, lfiTSl and HTSZ, ZlTSl and ZlTSZ, ZZTSl and Eli-T32, 2318i and 23TS2, respectively.

The Control Unit also includes a pair of transformers IT and Each of these transformers has three primary windings l'lhl, 1T '2 and lTPE and ZTPE, ZTPZ and ZTFS. The windings lTPl, lT-PZ and lTPS preterably have an equal number of turns as do the windings ZTPFL, ZTFZ, ZTPS. The primaries lTll, TYPE and 1TF3 are connected in a series network with corresponding pairs of the terminals 75 and '77 of Srl, 8Y2 and SYS with the pairs of terminals 75 and '77 sandwiched between the primary windings lTFl, ItTPZ and lTPS. This series n twork extends from one of the terminals 77 of SYl through lTPl, a conductor 83, the terminals 75- 1"? of 8Y2, a conductor 85, lTPZ, a conductor 57, the terminals of 8Y3, a conductor 89, llTPS, to the remaining term. ll '75 of SYll. The total potential impressed in series with the windings lTPl, lTPZ and lTPS of 1T is then equal to the vectorial sum of the potentials across the sandwiched terminals of SYll, 8Y2 and 8Y3.

The primaries Z-TPi, ETPZ and 2TP3 are similarly connected in a series sandwiched circuit with the remaining corresponding terminals 79 and 81 of SYl, SYZ and 8Y3. The transformer 1T has a plurality of secondaries ITSH, lTSlZ, iTSZl, ITSZZ, lTSEl and lTSElZ. The number of turns of these secondaries is equal to the number of turns on any winding of lTPl, lTPZ or TTP3. Thus, the potential across any secondaries lTSll through lTSSZ is equal to onethird the potential impressed across the primary windings lTPl, ITPZ and lTP3 or to the average potential across these windings. Transformer 2T has secondaries ZTSll, ZTSTLZ, ZTSZR, 21'822, ZTSSZ and ZTSSZ similarly related to the primaries ZTPl, ZTPZ and ZTPS.

The Control Unit includes a plurality of rcctiiiers of the bridge type 11R, 12R, 13R, 21R, 22R, 23R, 24R, 31R, 32R, Each rectifier is of the bridge type and has alternating-current input terminals and directcurrent output terminals. The secondaries lTSll and ZlTSl are connected to supply the alternating current terminals of 12R with the windings lTSiIl and ZlTSl so connected that the potentials across these windings add vectorially. In effect then, a potential equal to the vectorial sum of the average potential derived from one pair of terminals 75-77 each of SYl, 5Y2 and 8Y3 and the potential derived from the other set of terminals 7 9-8l of SYT. is impressed on the alternating current terminals of 121. Similarly, windings llTSl and ZTSlll are connected to the alternating current terminals of HR in such a sense hat the vectors representing their potentials are additive. in this case, the poretial impressed on the alternating current terminals of the rectifier HR is equal to the vector sum or" the average potential derivable from the pairs of terminals 79-81 of SYll, 8Y2 and 8Y3 and the potential derivable from the pair of terminals '7577 of 3Y1. The direct current output terminals of the rectitiers 11R and are connected to supply a resistor 161. The positive terminal of this resistor l-t l is connected to one terminal labeled i-A of the Winding WC of the magnetic amplifier MA of drive secondaries lTSlZl and ZlTSll are connected to supply rectifier 13R. In this case, the windings are so connected that the potential across the alternating current terminals of 13R is equal to the vectorial difference of the potentials across .lTSlZ and. ZTTSZ. The potential across the alternating current terminals of 133 is thus equal to the vectorial ditierence of the average potential across the corresponding pairs of terminals 7577 of SYl, SYZ and 8Y3 and the other pan of term nals 78l of SYl. Secondaries .rlTSZ- and ZTSlZ are similarly connected to 15R. Again the al nating potential across 14R is equal to the vectorial di "ercnce of the potential derivable from the corresponding pairs of terminals of SYl, 3Y2 and Y5 the remaining terminals 75-77 of SYl. The direct curr nt terminals of rectifers 13R and are connected to supply a resistor the positive terminals of which is connected to the remaining terminal of the winding WC of DRE which is labeled +B. +A and +3 are electrically positive relative to conductor connected to the negative terminals of 11R, 12R, 13R and 14 The polarity and magnitude of the current flow through WC is dependent on the relative magnitudes of the potentials across he corresponding resistors ltll Rectifiers and 21R, 23R and 24R, 32R and MR and 33R and are similarly connected in pairs to supply resistors 1557 and Trill, and 111i and lid respectively, the positive terminals of which are connected respectively to the conductors +6 +3 of the winding WC of the magnetic amplifier MA of DRZ and to conductors -+E and {F of the winding WC or" DRE. In each case, signals are produced proportional respectively to the sum of and the difierence between the average potential derived from one pair of output terminals and 77 or 79 and 81 or" the synchroties and the other pair of terminals 79 and $1 or 75 and '77 of one of the synchroties SYZ and 5Y3 respectively.

The average potential derivable from the corresponding pairs of terminals of 8Y1, SYZ and 3Y3 has a phase position dependent on the average phase position of the rotors 71 which, in turn, is dependent on the average posi tions of the cranks (not shown The sums and difierences derived serve to provide an error signal which when impressed on the corresponding magnetic amplifier MA so sets the corresponding generator G as to tend to correct for the deviation in position.

For an understanding of the relationship between the Vectors representing the various potentials and between the potentials themselves, FIGS. 5, 6, 7 and 8 should be considered. in FIG. 5 vector diagrams a, b and c present the potentials impressed on the brushes of the rotors '71 of the synchroties 5Y1, 3Y2 and 8Y3 respectively from the conductors Lil, L2 and L3. The corresponding potentials derivable from the secondary terminals 75-77 79-81 of the synchroties are in phase.

obtain vector V21.

.9 and 79- dl are represented in the vector diagrams d, e and f. VillTP corresponds to the potential derivable from one pair of terminals 5-77 of'SYl. -This potential is impressed across the-primary HTP as indicated by I the symbol. -V2lTP representsthe potential derivable from the other set of terminals 79-bit and impressed on ZlTP. The potentials-VlllTP and VZlTP are in quadr ture. Vl2TP, VZZTP, VET? and V23TP are similarly related. Diagrams d, e and 7- represent theinitial orstandby settings of the rotors ll in which VlltTP, VlZTP and,

currentterminals of the various rectifiers 11R through.

34R initially or during standby when the potentials derivable from corresponding pairs of terminals 7577 or In diagram a, VllTSl and VZTSM are presented vectorially. These vectors are added and their sum is V11. Diagram I) shows the addition of vectors VlZTSl and VZTSZlto V31 is similarly obtained. V11, V21 and V31are in phase. Similarly, vectors V12, V22 and V32 are shown in'diagrams a, b and c of FIG. 6

as the difference between V 11812 and VZlTSZ, V11 S22 tive conductor M5 is the rectified potential V11 or Vl2. The potential between +13 and NS is the rectifier potential V13 or V14. V11 and Vl-Z are equal as are also V1 3 and V14. Thus the potential difference between +A and +2 presented by the equation in FIG. 6 is zero. Similarly the potential difference between +C and +13 is zero and the potential difference between +13 and +F is zero. Thus with the synchroties in phase the windings WC of the magnetic amplifiers MA of each of the drives DRl, DRZ, DR?) are-not supplied with current.

FIG. -7 presents'the vector relationships which arise when there is a phase displacement between the rotors '71 of the synchroties SYll, SYZ and 8Y3. This figure is based on the assumption that during the operation, the phase position of the cranks have changed so that the crank of-drive DRE. leads the crank of drive DRE by approximately 22 /2 electrical degrees and the crank of drive DR3 lags the crank of DRZ by 22 /2 electrical degrees. The phase relationship of thepotentials derivable-from the related pairs of terminals of 8Y1, SYZ- and 8Y3 is presented in vector diagrams a, b and c. The summation of the vectors corresponding to the potentials VMTP, VlETP, VISTP derivable from corresponding pairs of terminals 7577 of thc-synchroties SYI, SYZ, 8Y3 is shown in diagram d. In this case, the vectors are added to produce a sum equalto-3V1TP. One-third of this sum is the average potential VllTS'which is the potential across any of the secondaries of IT. Similarly, VZTS is derivable by the summation of the vectors VZlTP, VQZTP and V231? which are the potentials derivable from the other corresponding pairs of terminals 79-8 1l of the synchroties 5Y1, SYZ-and 5Y3.

FIG. 8 presents a series of vector diagrams similar to those ofPiG. 6 but with the phase displacement corresponding to FIG. 7, a, b and 0, rather than zero displacement (Flt-3,5, d, e and 1). In this case, the vectors representing potentials derived from the transformers 1'1 and ET have a phase and magnitude equal to the average potentials VlTS and VZTS which are derived in diagrams D and E of FIG. 7. Thus, V2TS11 of-diagram a, FlG. 8, has a phase and magnitude equal to VETS of diagram e, PEG. 7. Similarly, VlTSlZ has a phase and magnitude equal to VllTS of diagram (1, FIG. 7. The potentials of the secondaries of transformers HT, 121, and HT, 2-1T, ZZT and 231 are represented by ltd vectors which in phase and magnitude arethe sameas the vectors representing the potentials V11-TP,'.V'12TP,

V13TP, VZETP, VZZTP and VZSTP of the corresponding primaries.

The vectorial sum of the various vectors in diagrams a, b, c, d, sand 1 of PEG. 8 areas represented in this view. Vll and V12 are new smaller than V13 and V14. The difference between the potentials derivable from-the rectifiers HR and .lZRand' 13R and MR (resistors ltliand ms is then a negative potential designated -Q in FIG. 8. V21, V22, V23 and V24 are all equal 1 so that the difference in the potentials derivable from the rectifier-s 21R and 22R and 23R and 24R (resistors N7 and Similarly, the diiference of and 33R and 3411 (resistors ill and 113) is a positive potential designated +Q in FIG. 8.

The potential supplied by the pairs of rectifierst 11R and 12R, 13R and MR, 21R and 22R, 23R and.24R, 31R and 32R and 33R and 34R is a relatively smoothdirectcurrent potential since in each case it is derived by rectifying twophase potentials, the separate compo nents of which are displaced by 90. The relatively small ripple does not affect the operation of'the appatus.

The potentials derivable from the various resistors are impressed across the windings .WC oi the amplifiers MA in the drives DRL D122 and D123. The potential impressed across winding WC of DRl has a polarity such that the current flows from +B- conductor to -]-A conductor and a magnitude proportional to the ditference of the absolute magnitudes of the vectors V13, VM and V11, V12. The winding WC of drive DRZ is supplied with no currentthrough conductors +0 and +D and the winding WC of drive DR? is supplied-with current flowing from conductor -l-E to conductor +F having a magnitude proportional to the difference between the absolute magnitudes of the vectorsVSiLVfiZ and V33, V34. The effect of this current flow through the various windings W0 is to cause drive DRll to'rotate slower than drive DRZ and driveBRE to'rotate at a higher speed than drive DR2 so that ultimately the drives are pulled into synchronisrn. During this position adjustment the effect of the speed control components of the respective drives may be such that all drivesare increasing in speed.

In the standby condition of the press line, the presses will be in the position in which they stopped duringthe prior operation. A press line of the type under considera tion here usually includes relays or other like means to assure that thepresses are stopped in an unloaded part of the cycle or stroke. It may be assumed then that the presses are stopped at some point between topdead center TDC (FIG. 3) and A. Thetransfcr mechanism is rnechanically tied to one of the presses,'for example to the leading press which operates on work W1 ofFlG. 1. With the press stopped between TDC and A the fingers Ziare inthe retracted position.

Inv standby the conductors L1, L2, and L3are congized. The synchroties 3Y1, SYZand SY3 may then be supplied with three-phase potential and two-phase potential may be derivable from their respective stators.

The rotors of these synchroties are positioned together corresponding to the positions of the associated presses. Potentials derived from corresponding pairs of terminals -77 and 7%431 of the synchroties SYl, SY2 and 3Y3 are then in phase. The drives DRL DRZ and DR3 are controlled from a starting circuit (not shown); Such a circuit would include contactors which would maintain the drives -DR1, DRZ and DR3 deenergized so long as a starting switch or pushbutton (not shown) is open.

To carry out an operation a stack of the raw material to be formed is placed adjacent to-the leading die in a aovaaoa position where the raw material units may be picked up one by one by the fingers 21. To start the operation the starting pushbutton (not shown) is closed energizing the drives DRl, DRE and DRS. Initially the windings WC of the magnetic amplifiers MA are not supplied with current since the secondary potentials VllTP, VlZTP, V131? and VZlTP, VZZTP, 123T? derivable from terminals 7577 and 79dl respectively of SYl, SYZ and 8Y3 are in phase. The drives DRil, DRZ and DR3 are controlled by the speed reference GS and since they are unloaded the motors M soon reach a speed corresponding to this reference. The motors M move the cranks which, in turn, move the presses. The presses being unloaded, the movement of the presses is substantially synchronized. At the point A (FIG. 3) the retraction of the fingers is started and at point B the fingers are completely retracted. Since none of the dies carries material to be formed the presses are unloaded as they are moved by the cranks from the point corresponding to B to BDC. The presses then remain in the same relative positions and continue to the point C.

At the point C, the fingers 21 start to move in. At this time the bars 23 are in the extreme left-hand position with respect to FIG. 1 and the fingers 21 associated with the leading press move towards the r w material. At point D the fingers associated with the leading press are fully engaging the first unit of the raw material. The movement now continues from D to A. At A the first unit of raw material is deposited on the leading press and the retraction of the finger 21 started. At B the fingers are retracted.

A unit of material (V1 is now seated on the leading die while the other dies continue unloading. As the motors M continue to rotate the drive Dill is subjected to a large load which reaches a maximum at bottom dead center BBC. The other drives are unloaded.

The effect on the drive DRll of the loading of the leading press is to reduce the speed of the corresponding motor M substantially. This, in turn, reduces the potential of the associated pilot generator PG so that current can flow through the variable resistor 51 and through the pilot generator PG of drive DRl. A portion of the potential from exciter GS is then absorbed reducing the reference speed potential supplied to the reference windings WSR of all amplifiers MA (FIG. 9). The speeds of the motors M of drives DRZ and D113 are then reduced substantially but since they are unloaded their speeds do not reach the low speed of the motor M of DRl. The leading press then is displaced in position with respect to the other presses and the phase of the potential derived from the synchrotie SYl is correspondingly displaced (lags) with respect to the potentials derivable from SYZ and 3Y3.

At point BBC, the leading press and drive DRl is unloaded. The speed of this press increases correspondingly permitting the speeds of the other presses to increase. Eventually, the speed of the leading press reaches a magnitude at which the associated pilot generator PG of drive DRl produces a potential such as to block current flow to the variable resistor 51. At this point the full potential of the speed reference generator GS takes effect so that the motors M of all drives DRE, D112 and D113 are permitted to reach full speed.

While this change of speed operation is taking place, the relative positions of the presses are also being shifted because of the operation of the Control Unit. Initially the leading press lags with respect to the presses driven by drives DRZ and D113 and thus with respect to the average position. The current flow through WC of drive DRll is then from +A to +3. Correspondingly the current flow through the winding WC of drives DRZ and DR3 respectively is from +D to -|C and from +F to +E respectively. The motor M of drive DRE then is accelerated at a higher rate than the motors of drives DR2 and DR3 and eventually the presses pull into l2 step. The presses are in step before point C is reached during the succeeding cycle.

As the motors M and the presses continue to move, the fingers 21 are again injected advancing the partly formed work W1 on the leading die to the second die and advancing raw material to the leading die. The above described process is then again repeated but this time two of the presses are loaded while the third is unloaded so that a correspondingly different change in speed and position takes place.

During the succeeding operation the first leading die is loaded With raw material, the second die with partly formed work from the first die and the third die with the partly formed work from the second die. Now all three presses are loaded and a corresponding operation involving the Control Unit and the Drive Unit takes place. The loading of the three presses may be difierent and the speeds and changes of positions introduced by the different loadings may be different. Whatever the relationship correction is effected by the Control Unit so that the presses are all together at the point C (FIG. 3).

At the end of an operation the leading press is first unloaded, the second press next and the third press last. The loading effect on the drives is then the converse to the effect produced at the start of an operation.

in HS. 10 a modification of this invention in accordance with its broader aspects is shown. This view relates to a system for operating only two press units or like apparatus. The Drive Unit in this case includes two drives DR@ and DR5. Each drive DRd and D115 has a magnetic amplifier MAE which has two position control windings WCE. and WCZ in addition to the other windings of the amplifiers MA.

The Control Unit in this case includes synchroties 5Y4 and 5Y5. Each synchrotie has a rotor 131 to which a three-phase potential is supplied from the conductors Ll, L2 and L3 and a two-phase stator 133. The potentials from the pairs of terminals of the stator of 8Y4 are supplied to transformers 41 and 5T respectively. The potentials of the synchrotie 8Y5 is correspondingly supplied to transformers 6T and '71 respectively. The secondaries dTSl and dTSl supply a rectifier 46R, the direct current terminals of which are connected between a conductor labeled +H and a common negative conductor 13S. Secondaries STSl and '7TS1 correspondingly supply a rectifier 57R which also supplies direct current potential between conductors +l-l and conductor 135. The current between conductors +H and 135 flow through windings WCZ of the magnetic amplifiers MAl. Secondaries dTSZ and TSZ and 5TS2 and '7TS2 are similarly connected to supply direct current between conductors +0 and 135 through rectifiers 64R and 75R. The current flow supplied by rectifiers R and 57R and 64R and R depends on the relative positions of synchroties 8Y4 and 8Y5 and effects an adjustment in the drives DR l and DRS so that they become synchronized during the unloaded part of their strokes or cycles.

To facilitate a complete understanding of the invention disclosed herein, the following summary is presented.

The invention in its specific aspects relates to apparatus for maintaining the angular position of the cranks of a plurality of presses within a given angular tolerance. The presses may be drawing, blanking or coining presses with each press obtaining energy from a flywheel to supple ment the synchrotie torque during the working portion of the press cycle. It is necessary for the speed of the press to decrease to release energy from the flywheel during the working cycle. Due to the press slowdown or speed regulation the angular velocity of the press crank is not constant. It is not desirable to have an angular position reference which has a constant angular displacement. It is desired to have an angular position reference which has an an ular position time characteristic similar to that attained on a press actually doing work during its load cycle. if a given press were to serve as master angular acres-ea position reference, it would be necessary to choose a press which is the average of the. presses in thevline in the amount of speed regulation. Even with choosing such a press its position reference would be incorrect when the press line is actually being loaded or unloaded. The press line is considered being loaded whenmaterial is being fed to. thestart of the line with the press-es at the end of the line having no material. The press line is considered being unloaded when no material is being fed to presses at the start of theline but material is still being worked at the end ofthe line. Toobtain a position reference which is not determined by the loading on any single press a reference which isthe average instantaneous angular position of all units is in accordance with this invention selected as a reference. This position reference signal is. then compared to the position signal of each press and a signal issent to the regulator corresponding to each 1 press indicating whether the press position involved is in phase ahead of, or behind, the position reference.

The unit which is coupled to the press crank shaft consists of awound rotorsynchrotie which has a three-phase primary and a two-phase secondary. FIGS. 4A, 4B and 4C. showth-e circuit diagram of three such position detection unitsSYll, SYZ and Y3. The primaryof each of theseunits is on the rotor 71 .andis excited from a common three-phase power supply Ll, L2 and L3. The two-phase secondary is on the stator member '73 in each case and has a voltage induced into it by the rotating field of. the primary member. The phase relationship between the primaryand secondary voltages in any synchrotie SYl,

. SYZ and 3Y3 or between secondaryvoltages of different units depends upon the. rotor position of thesynchrotie.

FIG. 5 shows the vector relationship of the primaries .and secondaries of. the synchroties- 5Y1, SYZ andSYS when thesynchro-ties are in the same relative position with respect toeach other. Since the primary 71 of each unit is excited from a common three-phase power supply :the 1 primary vectors are in phase and are represented, by

vectordiagrams a,.b and c. Vectordiagrams li e and f correspond to the stators '73. Since the primary is excited froma three-phase power supply tjhe .vectorsVZll, V12

\ .and Vll3,are rotating, rotation in.the counterclockwise direction being assumed. The. alternating current voltages induced into the, two-phasesecondaries 73 0f the synchroties. SYl, SYZ and 8Y3 are representable by rotati'ngvectors which rotate in the counterclockwise direction. NVith thesynchroties at rest the speed of rotation oftheprimary and secondary vectors is equal and if the power supply is 60 cyclesthey rotate at 607CYCl frequency.

In explaining the operation it is assumed that the .synchroties are of the four-pole type having rotating fields rotating at 1800 r.p.m., and that the synchrotiesare directly connected. tor-the crankshaft ofthe presses and the 1 press crankjshafts have a maximum speed of. revolutions per minute. It is also assumed that the direction of rotationof the rotors '71 of theseunits is counterclockwise.

Sincethe rotating field from the rotor '71 of each synchrotie andthe rotor are rotating in the same directi'on the speed of rotation of the flux onthe stator memher is 1825 revolutions per minute. I duced frequency of approximately 60.8 cycles per second This causes an into be introduced in the secondary ofeach synchrotie.

. The average position reference vector is obtained by addingvoltage vectors VllTP, VIZTP and VlEsTP veccto'rially and-dividing by 3. This is accomplished by addingthese voltages in sandwich series with three of the primary windings lTPTi, llTPZ and jlTPS. The division by the factor of 3 is obtain by turns ratio between the primary and secondary windings of transformers lTPl, 'ITPZ and 1TP3. Since there are three of these primary li ividual secondary winding is actually one-third the vector sum of primary voltages. In FIG. 5 it has been assumed that the secondary vectors of motors More in phase. The-secondary voltages derivedfrom 1T, are foreach secondary equal to VliTP, V12TP and VESTP. The vector for the secondary voltage IT is then the average vector of VllTP, V121"? and Vl3TP. This is a reference vector.

The same addition is applied to vectors of VZlTP, VZZTP and V23TP to arrive at a reference vector corresponding to each of the secondary voltages of 2T. This is also a reference vector which lags the reference vector from ET by 90 electrical degrees. Thus assume,

. and when VlllTP, VllZTP, V132"? are in phase VTTS: VMTP= VllZTP: Vll3TP similarly VETS: VZlTP: V22TP= V23TP To obtain an electrical signal which indicates the relative position of each press tothe, reference vectors a vector addition method is applied. Input to the regulators shown on FIGS. 4A, 4B and 4C can be described as push-pull two-phase signal error. FIG. 6 shows the vector relationships which exist with thethree synchroties in phase and are the vector sums of the potentials on transformer secondaries shown in FIGS. 4A, 4B and 4C. The polarities of the transformers are indicated in FIGS. 4A, 4B and4C. Four rectifiers are used in each of the three position signal circuits, Considering the circuit of synchrotie 8Y1, rectifiers 1111, 12R, 13R, 14R are included. Rectifiers 11R and 12R provide for a two-phase full-wave rectified signal between +A and 105 for .one side of the push-pull signal. Rectifiers 13 and 14 provide a two-phase fullwave rectified-signal for the one half of the push-pull signal between +13. and lltl5..- Vector diagram at on FIG. 6 shows the vector addition of VMTS andVZTSll to obtain V11 which is the voltage applied to rectifier 11R. Vector VlTSlZ and minus VZETS providesfor the vector sum of V12 which is the voltage applied to rectifier 12R.

Note that V11 and V12 are 90 apart in time, hence, the output voltage between +A and M35 is a full-waverrectifled two-phase potential with the magnitude of the. voltage between +A andltlS proportional to the magnitude of vectors V11 and V12.

In FIG. ,6, d shows the vectors for the voltages appearing across rectifiers ESR and MR, withVlS and V14 being the two-phase alternating-current voltage to be rectified by these two rectifiers to provide a ,twophase full- Wave rectified voltage output between +3 and 1&5. Since the magnitude of vectors V11, V12, V13 and V14 are all equal the potentional difference between +A.and +B is zero; hence, no corrective action is sent to the regulater for correction of position.

The vector relationship for DRZ and DR3 areshown in FIG. 6, b, c, e and 7. Since these drives are also assumed to be inphase they have duplicate outputs with zero output to amplifiers MA.

In FIG. 7 is shown anothercondition of the vectorrelationships to illustrate the signals. obtained, 8Y1, 22 /2 degrees ahead of 5Y2 and 8Y3, 22 /2 degrees behind SYZ. The corresponding vectors derived from. the secondaries of the synchroties 8Y1, 8Y2 and SYSareshown in diagrams a, b, c, of FIG. 7. FIG. 7, d shows the vector addition of VMTP, VlZTP and V13TP which divided by a factor 3 gives the average VlTS. The. magnitude of vector VlTS is now slightly less than the magnitude of VlllTP, VllZTP or VTSTP. This decrease in magnitude of the vector, however, does not affect the operation of the circuit since it appears in both phases of the twophase circuit by the same amount. The phase relationship between the voltages for Vii and VTZ is still 90 and since the signal to the regulators is obtained from the push-pull circuit by comparing the magnitudes of V11, V12 to the magnitudes of V3.3 and V14, both sides of the push-pull circuit are slightly attenuated by this decrease in magnitude of VHS and VZTS and no net result except for a slight decrease in output signal occurs. In actual practice, the maximum displacement angle is anticipated to be approximately 10 electrical degrees instead of 22 /2; this gives a magnitude of VETS of 99% of the magnitude of VHTP, VilZTP or VllZiTP. Since the affect of the smaller magnitude of VlTS vector has negligible affect on the performance of the system for the ease of explanation of the operation no decrease is assumed. The VZTS reference vector is again obtained in the same manner as the V 1T8 vector (see KG. 7, e). VZTS vector lags VETS vector by 90 electrical degrees.

FIG. 8 shows the same addition of vectors as is shown in FIG. 5 except for the ahead of and behind phase positions of 8Y1 and 8Y3 units. Referring to FIG. 8 a vector V11 is obtained by the addition of VlitTSll and VZTSlll. Vector V12 is obtained by the addition of minus VZlTS7 and VTTSTZ. Note that the V11 and Vii vectors are still 90 degrees apart in time and their magnitudes have been diminished due to the vector addition of the different an ular relationship between the position vectors VllTSi and minus VZTTSZ in respect to the reference vectors V iTSiZ and VZTSH. FIG. 8, d gives the vector additions of VlTSllli, an average, and VZTTST from which is obtained vector V313, and of minus VZTSTZ, an average, and VlIiTSZ from which is obtained vector V14. V13 and Vld vectors are 90 degrees apart in time. The rectified voltage at +A to lldS is now proportional to the magnitude of the V11 and V12 vectors. The rectified voltage at -]-B to 185' is now proportional to V13 and V14 vectors which are considerably larger than the V11, V12 vectors. Therefore, +13 is at a higher magnitude than +A and the current signal is supplied to the drive DR with current flowing from +B to +A. This signal is of such an affect as to slow down press drive DRll to bring its position back to the reference position.

Since each of the three press signal arrangements are identical, a study of drive DRE of PEG. 8 shows the affect of any unit being behind the average position. Referring to FIG. 8, c, the magnitude of voltage at +13 is proportional to vector V31 and V32 and greater than the magnitude of the voltage at +F which is proportional to vectors V33 and V34. Since the voltage at +E is greater than the voltage at +F, current flows from E to F through the regulator R3 which is in the opposite direction to the flow obtained for drive DRl and is now in a direction such as to increase the speed of the third press. Since the vectors V21 and V22, and V233 and V24 are of the same magnitude the same potential exists at +C and +D and no corrective action is required for drive DRZ.

By the use of the two-phase rectified power supplies for obtaining corrective signals to the drives a direct current supply with much less ripple than would be obtained with single phase rectified supplies is obtained. Filters are necessary to filter the ripple voltage from the signal currents to the drives DRl, DRZ, D113, but with the greatly reduced ripple. By using the two-phase systems little time delay is induced by the filters.

The push-pull arrangement of obtaining signals for +A and +3, +C and +D, and +E and +1 has an advantage in that any regulation or change in magnitude of voltage due to attenuation in adding and averaging reference vectors or change in voltage due to rotational speed of the position detecting synchroties are compensated. The advantage of connecting the primaries of the transformers for reference vectors in sandwich series with the various voltages from the synzhroties 8Y1, 8Y2 and 5Y3 allows a much greater range in the output voltages of the secondaries of these synchroties without exceeding low volt age class of insulation level. It also allows, if required, with simple switching to eliminate one or more of the press drives from the line.

In accordance with this invention, an angular position reference which is dependent upon the average angle of all units and a position error signal which is proportional to the actual angular error of each press in respect to the reference, with the signal being zero for correct position and of different polarities for ahead and behind positions is provided. This arrangement also obtains a signal which is practically linear with angular error and which is not affected by change of rectifier resistance since all rectifiers are operating in a region where their forward resistance is practically constant because of the phase rectification.

FIG. 10 shows a modification of the invention in accordance with its broader aspects applicable where only two presses are required to operate. This arrangement of only two presses does not require the obtaining of the average reference vectors but compares only the relative vectors between the two presses. The output arrangement on FIG. 9 is shown as connected to two control windings WCi and WCZ of magnetic amplifiers MAI of drives DRd and DRE). In this arrangement the flux addition of the two windings on each amplifier gives the net results of the push-pull output of +6 and +11 to 135. In this arrangement the polarities of the control windings of one drive DR4 are reversed with respect to those of the other drive DB5 such that the current flows from 5 to (hand 6 to 5 or '7 to 8 and 8 to 7 (see FIG. 10).

The press position circuits are shown with three-phase primary excitation. This excitation may be any polyphase number which would produce a rotating field. The rotating field is shown on the rotor structure; the field may be applied to either the stator or the rotor in accordance with the broader aspects of this invention. The output of the synchroties SYl, 5Y2 and 5Y3 is shown as twophase on both FIGS. 4A, 4B, 4C and 10; they could also be single phase, three-phase, or any other polyphase output. The regulating components shown as magnetic amplifiers in FIGS. 4A, 4B, 4C and 10 may be Rototrol units in accordance with the broader aspects of this invention. Position reference units which have polyphase output other than two-phase may in accordance with the broader aspects of this invention be fed into a transformer arrangement obtaining a two-phase voltage for obtaining and measuring the position reference and position error quantities.

In FIGS. 4A, 4B, and 40 the error signals are supplied through +A and +8, +C and +D, +E and +F. Since these are all of positive polarities and are obtained from rectifiers it is necessary to use loading resistors between +A and Th5 and between +B and 105. In FIG. 10 the outputs of the position error circuit from both sides of the push-pull arrangement are fed into separate windings. A magnetic addition of flux occurs in the amplifiers MAT of FIG. 10 and the resulting fiux developed by the two windings supplies the error correction signal.

While a preferred embodiment of this invention has been disclosed herein, many modifications thereof are feasible. The invention, then, is not to be restricted except insofar as is necessitated by the spirit of the prior art.

We claim as our invention:

1. A control system for apparatus for treating work progressively in a plurality of positions, said apparatus including means at each of said positions for treating said work and drive means connected to each of said treating means for actuating said treating means, the said control system including position regulating means connected to each of said drive means for adjusting the position of the associated drive means, means connected to each of said drive means for deriving a signal dependent on the position of the associated drive means, means connected to said signal deriving means of all of said drive means for deriving a signal corresponding to the average of the position dependent signals of all of said drive means, means connected to each of said position dependent signal deriving means and to said average signal deriving means for deriving for each drive means a signal dependent on the algebraic difference between said average signal and the position dependent signal for the associated drivemeans, and means connected to each of said regulating means and to the associated difference signal deriving means for causing said regulating means to set the associated drive means to the position corresponding to said average signal.

2. In combination a first drive shaft, a second drive shaft, a third drive shaft, first, second and third means connected to said first, second and third shafts respectively, for deriving first, second and third signals dependent on the respective positions of said first, second and third shafts, means connected to said first, second and third means for deriving a signal dependent on the average of said first, second and third signals, first, second and third differential means connected to said average signal deriving means and to said first, second and third position signal deriving means for deriving first, second and third error signals dependent on the algebraic differences between said average signal and said first, second and third position signals respectively, first, second and third regulator connected to said first, second and third shafts respectively for adjusting the positions of said shafts, and means connected to said first, second and third regulators for impressing on said regulators said first, second and third error signals respectively to cause said regulators to adjust their respective shafts so as to suppress the associated error signals.

3. A control system for apparatus for treating work progressively in a plurality of positions, said apparatus including means at each of said positions for treating said Work and drive means connected to each of said treating means for actuating said treating means, the said control system including, means connected to each of said drive means for deriving a signal dependent on the position of the associated drive means, means connected to said signal deriving means of all of said drive means for deriving a signal corresponding to the average of the position dependent signals of all of said drive means, means connected to each of said position dependent signal deriving means and to said average signal deriving means for deriving for each drive means a signal dependent on the algebraic difference between said average signal and the position dependent signal for the associated drive means, and means connected to each of said drive means and to the associated difference signal deriving means for setting the associated drive means to the position corresponding to said average signal.

4. in combination first, second and third drive shafts, means connected to said drive shafts for deriving a signal dependent on the average position of said drive shafts referred to a starting position of said shafts, first, second and third differential means connected to said average signal deriving means and to said first, second and third shafts respectively for deriving first, second and third error signals respectively dependent on the algebraic deviation of each of said shafts from its said starting position, and first, second and third correcting means connected to said first, second and third shafts respectively and to said first, second and third difi'erential means respectively, for correcting the positions of said first, second and third shafts so as to suppress its associated error signal.

5. A control system for apparatus for treating worlc progressively in a plurality of positions during a plurality of steps, the said apparatus including means at each of said positions for treating said work and drive means connected to said treating means for actuating said treating means, each of said steps consisting of a cycle during one portion of which said work is treated and each said drive means is subjected to a high load, said high load being different for different drive means, and during the remaining portion of which said work is advanced from one said position to the succeeding said position, said drive means being subjected to a low load during said remaining portion, the said system comprising means con; nected to all said drive means for continuously deriving an average signal dependent of the average relative position of all said drive means, means connected to each said drive means and to said average signal producing means for deriving for each drive means an error signal dependent on the deviation of said last-named drive means from said average position, and means connected to each said error signal deriving means and to each said drive means for continuously applying the associated said error signal to each said drive means to correct the position of said last-named drive means so as to suppress said error signal.

6. In combination first drive means, second drive means, means for producing a speed reference signal, first means connected to said first drive means and to said signal producing means responsive to said signal for maintaining the speed of said first drive means at a magnitude corresponding to said signal, second means connected to said second drive means and to said signal producing means responsive to said signal for maintaining the speed of said second drive means at a magnitude corresponding to said signal, first means connected to said first drive means, to said signal producing means and to said first and second signal responsive means for absorbing a part of said signal external to said signal responsive means when the speed of said first drive means is reduced below a predetermined magnitude so that said first and second responsive means react with a signal corresponding to said last-named speed, and second means connected to said second drive means, to said signal producing means and to said first and second signal responsive means for absorbing a part of said signal external to said signal responsive means when the speed of said second drive means is reduced below a predetermined magnitude, so that said first and second responsive means react with a signal corresponding to said last-named speed.

7. In combination first drive means, a first tachometer connected to said drive means for producing a first potential corresponding to the speed of said drive means, second drive means, a second tachometer connected to said second drive means for producing a second potential corresponding to the speed of said second drive means, first rectifier means, second rectifier means, means producing a speed reference potential, impedance means, means connecting in series said reference potential, producing means, said impedance means, said first rectifier means and said first tachometer, with said first rectifier means poled to conduct under said reference potential and to block under said first potential, means connecting in series said reference potential producing means, said impedance means, said second rectifier means and said second tachometer, with said second rectifier means connected to conduct under said reference potential and to block under said second potential, first regulator means including a speed reference winding, a speed signal Winding and an output winding, second regulating means including a speed reference winding, a speed signal winding, and an output winding, means connecting in a first series circuit said speed reference potential producing means, said impedance means, and said speed reference winding of said first regulator means, means connecting in a second series circuit said speed reference potential producing means, said impedance means, and said speed reference Winding of said second regulator, means con necting in a third series circuit said first tachometer and said speed signal winding of said first regulator means, means connecting in a fourth series circuit said second tachometer and said speed signal winding of said second regulator means, the ampere turns through said speed reference windings in said first and second circuits counteracting the ampere turns through said speed signal windings in said third and fourth circuits respectively, means connecting said output winding of said first regulator to said first drive means in regulating relationship therewith, and means connecting said output winding of said second regulator to said second drive means in controlling relationship therewith.

8. In combination first, second and third drive shafts, speed regulating means connected to said'drive shafts for maintaining said shafts at a predetermined spee when all said shafts have a speed not loaded substantially lower than said speed and for permitting all said shafts to drop to a lower speed when at least one of said shafts drops substantially below said predetermined speed, means connected to said drive shafts for deriving a signal dependent on the average position of said drive shafts referred to a starting position of said shafts, first, second and third differential means connected to said average signal deriving means and to said first, second and third shafts respectively for deriving first, second and third error signals respectively dependent on the algebraic deviation of each of said shafts from its said starting position when said shafts are operating at said lower speeds, and first, second and third correcting means connected to said first, second and third shafts respectively and to said 255i first, second and third differential means respectively, for correcting the positions of said first, second and third shafts so as to suppress its associated error signal while increasing the speeds of said shafts to said predetermined speed.

9. In combination first drive means, second drive means, means for producing a speed reference signal, first means connected to said first drive means and to said signal producing means responsive to said signal for maintaining the speed of said first drive means at a magnitude corresponding to said signal, second means connected to said second drive means and to said signal producing means responsive to said signal for maintaining the seed of said second drive means at a magnitude corresponding to said signal, and means connected to said first drive means, to said signal producing means and to said first signal responsive means for absorbing a part of said signal external to said signal responsive means when the speed of said first drive means is reduced below a predetermined magnitude so that said first and second responsive means react with a signal corresponding to said last-named speed.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A CONTROL SYSTEM FOR APPARATUS FOR TREATING WORK PROGRESSIVELY IN A PLURALITY OF POSITIONS, SAID APPARATUS INCLUDING MEANS AT EACH OF SAID POSITIONS FOR TREATING SAID WORK AND DRIVE MEANS CONNECTED TO EACH OF SAID TREATING MEANS FOR ACTUATING SAID TREATING MEANS, THE SAID CONTROL SYSTEM INCLUDING POSITION REGULATING MEANS CONNECTED TO EACH OF SAID DRIVE MEANS FOR ADJUSTING THE POSITION OF THE ASSOCIATED DRIVE MEANS, MEANS CONNECTED TO EACH OF SAID DRIVE MEANS FOR DERIVING A SIGNAL DEPENDENT ON THE POSITION OF THE ASSOCIATED DRIVE MEANS, MEANS CONNECTED TO SAID SIGNAL DERIVING MEANS OF ALL OF SAID DRIVE MEANS FOR DERIVING A SIGNAL CORRESPONDING TO THE AVERAGE OF THE POSITION DEPENDENT SIGNALS OF ALL OF SAID DRIVE MEANS, MEANS CONNECTED TO EACH OF SAID POSITION DEPENDENT SIGNAL DERIVING MEANS AND TO SAID AVERAGE SIGNAL DERIVING MEANS FOR DERIVING FOR EACH DRIVE MEANS A SIGNAL DEPENDENT ON THE ALGEBRAIC DIFFERENCE BETWEEN SAID AVERAGE SIGNAL AND THE POSITION DEPENDENT SIGNAL FOR THE ASSOCIATED DRIVE MEANS, AND MEANS CONNECTED TO EACH OF SAID REGULATING MEANS AND TO ASSOCIATED DIFFERENCE SIGNAL DERIVING MEANS FOR CAUSING SAID REGULATING MEANS TO SET THE ASSOCIATED DRIVE MEANS TO THE POSITION CORRESPONDING TO SAID AVERAGE SIGNAL. 